Vacuuming Device Comprising a Vacuum Cleaner and a Bag Filter

ABSTRACT

The invention relates to a vacuum-ceaning apparatus comprising a vacuum cleaner and a filter bag made of non-woven fabric, wherein the vacuum cleaner has a nominal electric input power of less than 1200 W, preferably less than 1100 W, more preferably less than 900 W, wherein the vacuum cleaner comprises a motor-fan unit and a controlling device controlling the vacuum cleaner such that the airflow is kept substantially constant at a value of at least 34 l/s, preferably substantially constant at a value of at least 37 l/s, more preferably substantially constant at a value of at least 40 l/s when the filter bag is loaded with DMT8 test dust analogous to EN 60312, and wherein the filter bag is a disposable filter bag made of non-woven fabric which has an airflow drop of less than 15%, preferably less than 10%, more preferably less than 5% in tests demonstrating the reduction of the maximum airflow with a partially filled dust container analogous to EN 60312.

FIELD OF THE INVENTION

The invention relates to a vacuum-cleaning apparatus comprising a vacuumcleaner and a filter bag made of non-woven fabric.

DEFINITIONS

The description of the prior art and the invention is based on thestandards, definitions and measuring methods specified below:

EN 60312: EN 60312 denotes the standard in version EN 60312:1998+A1:2000 A2:2004.

EN 60335: EN 60335 denotes the standard in version EN 60335-2-22010.

Determination of air data: The air data of a vacuum cleaner aredetermined according to EN 60312, chapter 2.8. The measuring device Baccording to chapter 5.2.8 is used. if motor-fan units sob are measured,viz. without a vacuum cleaner case, the measuring device B is appliedequally.

The measurement of the reduction of the maximum airflow with a partiallyfilled dust container according to chapter 2.9 is carried out withorifice 8 (40 mm).

Nominal electric input power of a vacuum cleaner: The input power of avacuum cleaner is determined according to EN 60335. According to EN60335 and EN 60312 the input power is denoted with P₁. According to EN60335 the nominal input power is the arithmetic mean from the maximuminput power and the minimum input power. The maximum input power ismeasured at the highest airflow (open airflow), and the minimum inputpower at an airflow of 0 l/s (sealed suction), Electromotively drivenattachments such as brushes and the like are disregarded in the inputpower determination.

Airflow: According to EN 60312 the airflow is determined using theversion B measuring chamber. In the prior art this airflow is often alsoreferred to as volume flow or suction airflow.

Airflow drop, constant airflow: The airflow drop is determined inusability tests of vacuum cleaners following EN 60312 (chapter 2.9 ofthis standard) using the version B measuring chamber. Deviating from thestandard the reduction of the airflow is tested by vacuuming 400 g ofDMT8 test dust in 50 g portions, provided the highest usable volume ofthe filter bag (see chapter 2.7 of this standard) is above 2 l. Thethree conditions described in chapter 2.9.1.3 of the standard as leadingto the discontinuation of the test are disregarded. Chapter 2.9.1.3 isrelevant for volumes below 2 l. This method of measuring the airflowdrop thus modified as against the EN 60312 standard will be referred toas “analogous to EN 60312” in the present description and the presentpatent clairns.

A constant airflow q is assumed if the airflow q_(c) is not lower afterthe vacuuming of the DMT8 test dust than the airflow q_(max) with anempty dust container (cyclone vacuum cleaner), respectively empty filterbag (bag vacuum cleaner). Typically, 400 g of DMT8 test dust arevacuumed in 50 g portions. The test is performed with orifice 8 (40 mm).With regard to the definition of the term orifice reference is made toEN 60312, chapter 5.2.8.2. This orifice corresponds to a relatively openfloor nozzle. The airflow drop is calculated according to:

Airflow drop [%]=((q_(max).q_(c))/q_(max))×100

-   -   q_(max)=maximum airflow with empty dust container    -   q_(c)=maximum airflow with partially filled dust container

However, in the present description of the prior art and the invention asubstantially constant airflow does not mean that the airflow remainsconstant in different working situations, e.g. the vacuuming of carpetedfloors, respectively hard floor surfaces, or the vacuuming withaccessory nozzles. The different orifice areas of these nozzles and thedifferently strong reduction of this orifice area on different floorcoverings result in different airflows, depending on the workingsituation. With respect to EN 60312 this would correspond to a test withdifferent orifices, with orifice 0 corresponding to a state with adogged nozzle, Orifice 9 (50 mm) corresponds to a nearly unobstructedinflow. Current floor nozzles typically have an operating point in therange of orifice 7 (30 mm) to 8 (40 mm).

Power increase of the fan motor: The power increase of a fan motorimplies an increase of the input power [W]. In a universal motor thepower is adjusted by a phase-angle control, In the SR motor (see below)the control voltage of the motor is controlled,

SR motor: An SR motor is a switched reluctance motor which ischaracterized by a simple and robust construction and high possiblespeeds (>100,000 rpm). The torque is generated by the reluctance force.

Flat bags: Rat bags as used in the present invention are filter bagswhose filter bag wall comprised of two individual layers of a filtermaterial with identical surface areas is formed such that the twoindividual layers are connected to each other only at theircircumferential edges (the term identical surface area does notpreclude, of course, that the two individual layers differ from eachother by the fact that one of the layers includes an inlet opening).

The connection of the individual layers may be realized by a weldingseam or adhesive seam along the total circumference of the twoindividual layers. However, it may also be realized such that oneindividual layer made of a filter material is folded about one of itsaxes of symmetry while the other, open circumferential edges of the socreated two sub-layers are welded or bonded to each other (so-calledtubular bag). Thus, this type of manufacture requires three welding orbonding seams. Two of those seams then form the filter bag edge. Thethird seam may equally form a filter bag edge or he on the filter bagsurface.

Flat bags as used in the present invention may also comprise so-calledgussets. These gussets may be fully unfoldable. A flat bag having suchgussets is shown, for instance, in DE 20 2005 000 917 U1 (see FIG. 1with folded gussets, and FIG. 3 with unfolded gussets). Alternatively,the gussets may be welded to sections of the circumferential edge. Sucha flat bag is shown in DE 10 2008 006 769 A1 (see FIG. 1 thereof).

Surface folds: A filter bag whose filter bag wall comprises surfacefolds is known per se from the prior art, e.g. from the European patentapplication 10163483.2 (see in particular

FIG. 10 a and FIG. 10 b, respectively FIG. 11 a and FIG. 11 b thereof).If the filter bag wall comprises a plurality of surface folds thismaterial is also called a pleated filter material. Such pleated filterbag wags are shown in the European patent application 10002964.4.

FIG. 1 and FIG. 2 show a cross-section of a filter bag comprising a wallwith two surface folds. Such surface folds enlarge the filter surface ofthe filter bag so that a higher dust absorption capacity of the filterbag, along with a high collection efficiency and longer service life, isobtained (as compared with a filter bag having same outer dimensions andwithout surface folds).

FIG. 1 shows a filter bag 1 comprising a filter bag wall 10 with twosurface folds 11 in the form of so-called dovetail folds. The figureshows a cross-section of the filter bag through the filter bag center.The longitudinal axes of the surface folds accordingly extend in oneplane which, again, extends perpendicular to the plane of projection,and the surface folds extend at theft longitudinal ends into the weldingseams of the filter bag which extend in parallel to the plane ofprojection and are positioned in front of and behind the plane ofprojection. Thus, the strongest unfolding of the surface folds is in themiddle thereof. The filter bag is here shown in a state in which thesurface folds are already unfolded to some extent.

FIG. 2 shows a filter bag 2 comprising a filter bag wall 20 with twosurface folds 21 in the form of so-called triangular folds. The figureshows a cross-section of the filter bag through the filter bag center.The longitudinal axes of the surface folds accordingly extend in oneplane which, again, extends perpendicular to the plane of projection,and the surface folds extend at theft longitudinal ends into the weldingseams of the filter bag which extend in parallel to the plane ofprojection and are positioned in front of and behind the plane ofprojection. Thus, the strongest unfolding of the surface folds is in themiddle thereof. The filter bag is here shown in a state in which thesurface folds are already unfolded to some extent.

Apart from the surface folds illustrated in FIG. 1 and FIG. 2 surfacefolds having different shapes are feasible, too. It should not beregarded as a limitation that the surface folds in the embodiments ofFIG. 1 and FIG. 2 extend perpendicular to a bag edge. Of course, thesurface folds may also extend at an angle to the bag edges.

Suction power: The suction power is the product of negative pressure[kPa] and airflow [l/s]. According to EN 60312 the suction power isdenoted with P₂.

Efficiency: The efficiency of a vacuum cleaner or a motor-fan unit isdetermined in accordance with EN 60312, chapter 2.8.3.

PRIOR ART

The requirements made on vacuum-cleaning apparatus have been subject toconsiderable change in recent years.

One essential point expected by the users of vacuum-cleaning apparatusis that the vacuum-cleaning apparatus produces a constant airflow evenas the dust load increases or, in other words, that the vacuum-cleaningapparatus does not experience an airflow drop as the dust loadincreases.

The study by “AEA Energy & Environment Group” on behalf of the “EuropeanCommission Energy” for the definition of the requirements on an ecodesign for vacuum cleaners demonstrates that it would be desirable tolimit the input power to below 1100 W in the future for energy policyaspects. The users of vacuum cleaners do expect, however, that thecleaning performance will not significantly deteriorate as compared tovacuum-cleaning devices with a substantially higher input power as areavailable nowadays.

The customers' hygiene requirements on a vacuum-cleaning apparatusrelate no longer to a lowest possible dust emission of the apparatusonly, but also to the hygienic disposal of the vacuumed dust.

In terms of the collection concept a difference is made between vacuumcleaners without filter bags and vacuum cleaners with filter bags. Theseapparatus each have typical advantages and disadvantages.

Vacuum cleaners with filter bags are characterized by a high airflow.However, as the filter bag is more and more loaded the airflow dropsmore or less strongly. Approximately up to the year 2000 filter bagsmade of paper were primarily used. In tests demonstrating the reductionof the maximum airflow with a partially filled dust container analogousto EN 60312 such paper filter bags show an airflow drop of about 80%(respectively 60% if an internal tissue is used). After that, filterbags having non-woven fabric inserts slowly began establishingthemselves. Initially, filter bags with non-woven fabric layers of a lowdust storage capacity were used (SMS filter bags). By introducing filterbags of non-woven fabrics with a capacity layer it was possible toclearly reduce this drop of the airflow (see EP 0 960 645). In testsdemonstrating the reduction of the maximum airflow with a partiallyfilled dust container analogous to EN 60312 such filter bags show anairflow drop of approximately 30%. Further enhancements were achieved byan advance filtration by loose fibers in the bag (DE 10 2007 060 747, DE20 2007 010 692 and WO 2005/060807) or an advance separation by a bag inthe bag (WO 2010/000453, DE 20 2009 002 970 U1 and DE 20 2006 016 303U1). Flow deflections and flow distributions in the filter bag areproposed in EP 1 915 938, DE 20 2008 016 300, DE 20 2008 007 717 Ul(dust-storing liner), DE 20 2006 019 108 U1, DE 20 2006 016 304 Ul, EP 1787 560 and EP 1 804 635. In tests demonstrating the reduction of themaximum airflow with a partially filled dust container analogous to EN60312 an airflow drop of approximately 15% was achieved with such filterbags. Thus, a further improvement of the suction power stability isobtained. The European patent applications 10002964A, 10163463.2, and10163462.2 disclose an improved dust storage capability by pleating thefilter material or by providing so-called surface folds. The Europeanpatent application 10009351.7 shows how the suction power stability canbe improved by an optimized positioning of the bag in the vacuumcleaner. Thus, in the tests demonstrating the reduction of the maximumairflow with a partially filled dust container analogous to EN 60312filter bags of this type show an airflow drop of about 5%.

With regard to the hygienic disposal of the vacuumed dust, holdingplates were developed by means of which the filter bag, prior toremoving it from the vacuum cleaner, is tightly sealed manually,semi-automatically or automatically. (e.g. EP 2 012 640).

Vacuum cleaners without bags—in particular cyclone vacuum cleaners—arecharacterized by a substantially constant airflow as the dust collectingcontainer is loaded with dust. At first sight, the constant airflow of acyclone vacuum cleaner is an advantage, compared to vacuum cleaners withfilter bags which get clogged more or less strongly as the load of thefilter bag increases so that the airflow is reduced correspondingly.However, this is bought by a very high nominal electric input power ofthe cyclone vacuum cleaners. This high input power is necessary owing tothe high losses brought about by the separating principle, namely theloss for the maintenance of the high rotational speed of the dust-ladenair in the cyclone separator.

By combining a number of cyclone separators to multi-stage cyclones itwas attempted to increase the efficiency and the separating efficiency(EP 0 042 723). With such vacuum-cleaning apparatus an aelow of 33 l/scan be achieved. However, this is opposed by a nominal electric inputpower of far more than 2000 W. Cyclone vacuum cleaners having anelectric input power of approximately 1400 W allow the realization of anairflow of about 25 l/s.

With conventional vacuum-cleaning apparatus working with filter bags,freshly inserted and empty, it is nowadays possible to realize anairflow of approximately 40 l/s. Such vacuum cleaners have a nominalinput power of about 1300 W.

However, the airflow strongly decreases with the dust loading, as can beseen in FIG. 3. FIG. 3 shows the reduction of the airflow in response tothe vacuumed amount of DMT8 dust analogous to EN 60312 in knownapparatus with filter bags (e.g. Miele S5210 with a nominal electricinput power of 2200 W and different filter bags of a non-woven fabric)and without filter bags (Dyson DC23 alergy with a nominal electric inputpower of 1400 W).

In addition to improvements of the filter bags approaches have been madeto realize a constant airflow in vacuum cleaners with filter bags bymeans of an electronic control.

A vacuum-cleaning apparatus is described, for instance, in U.S. Pat. No.4,021,879, whose vacuum cleaner comprises a controlling devicecontrolling the vacuum-cleaning apparatus in such a way that asubstantially constant airflow is realized. However, in this apparatusfilter bags made of paper are used. Owing to the great clogging tendencyof filter bags made of paper (about 80% airflow drop with 400 g of DMT8;inner tissues were not used as yet at the publication date of U.S. Pat.No. 4,021,879) a very broad control range has to be provided for thenominal electric input power. Although a constant airflow is thustheoretically realizable, same is very low. For this reason, thisconcept was not pursued and, therefore, could not be implemented in aproduct successful on the market.

DESCRIPTION OF THE INVENTION

Given the aforementioned disadvantages of the prior art the invention isbased on the object to provide a vacuum-cleaning apparatus in which aconstantly high airflow is realized despite a low nominal electric inputpower.

This object is achieved by a vacuum-cleaning apparatus comprising thefeatures of patent claim 1, viz. by a vacuum-cleaning apparatuscomprising a vacuum cleaner and a filter bag made of non-woven fabric,wherein the vacuum cleaner has a nominal electric input power of lessthan 1200 W, preferably less than 1100 W, more preferably less than 900W, the vacuum cleaner comprises a motor-fan unit and a controllingdevice controlling the vacuum cleaner such that the airflow is keptsubstantially constant at a value of at least 34 l/s, preferablysubstantially constant at a value of at least 37 l/s, more preferablysubstantially constant at a value of at least 40 l/s when the filter bagis loaded with DMT8 test dust analogous to EN 60312, and the filter bagis a disposable filter bag made of non-woven fabric which has an airflowdrop of less than 15%, preferably less than 10%, more preferably lessthan 5% in tests demonstrating the reduction of the maximum airflow witha partially filled dust container analogous to EN 60312.

The present invention is based on the concept that a vacuum-cleaningapparatus with a filter bag, viz. an empty filter bag, is operated withan input power that is adjusted to be lower than the maximum power ofthe motor, so that the input power of the motor can be increased incorrespondence with the increasing load of the filter bag. Surprisingly,it has shown that only with filter bags having a clogging tendency ofless than 15%, preferably less than 10%, more preferably less than 5% arelatively small increase of the input power of the motor is necessaryto keep the airflow constant on a level required for the efficientvacuum-cleaning, i.e. at least 34 l/s. Only thus had it been possible torealize a vacuum-cleaning apparatus that can provide a substantiallyconstant volume flow as the filter bag is continuously loaded, while, atthe same time, the maximum electric input power of the vacuum cleanerremains below a predetermined value of 1200 W which is acceptable fromthe viewpoint of power consumption.

According to a further development of the above-described invention thevacuum-cleaning apparatus comprises an electronic controlling devicewhich is adapted to control the electric input power of the motor-fanunit.

Preferably, the apparatus is then adapted such that the increase of theinput power of the motor-fan unit required to maintain the substantiallyconstant airflow when the filter bag is loaded with DMT8 dust analogousto EN 60312 is not more than 35%, preferably not more than 20%, and morepreferably not more than 15% in relation to the input power of themotor-fan unit when the filter bag is empty. According to thisembodiment it is possible to realize vacuum-cleaning apparatus with aconstant airflow, with a vacuuming behavior as is known from today'snon-controllable apparatus, whereby the future energy policy standardscan be satisfied without problems.

Particularly suited for such an apparatus is a motor-fan unit comprisinga reluctance motor, preferably a switched reluctance motor. Such motorsare characterized in particular by their robustness and durability.

Alternatively, according to another preferred further development of theinvention an apparatus may be provided wherein the controlling devicecomprises a throttle valve which controls the airflow to besubstantially constant.

In both alternative further developments of the controlling device thecontrolled variables may be the negative pressure downstream of thefilter bag, the negative pressure upstream of the filter bag or the flowrate measured at an optional position in the flow path. Optionalcombinations of these three quantities are also feasible.

According to a preferred further development of all inventions describedabove the filter bag may be provided in the form of a flat bag. The flatbag shape is the most widely spread shape for non-woven bags as bags ofthis shape are very easy to manufacture. As opposed to the paper filtermaterial used for paper filter bags the non-woven fabric material isvery hard to fold permanently owing to the great resilience, so that themanufacture of more complex bag shapes, such as block bottom bags orother bag shapes having a bottom, is very complicated and expensive.

Particularly suited for use in the apparatus according to the inventionare vacuum cleaner bags having a pleated filter material or surfacefolds. Such vacuum cleaner bags are characterized by a particularly lowairflow drop.

According to a preferred further development of the invention themotor-fan unit is adapted such that the vacuum cleaner generates, with afilter bao being inserted, with an orifice 0 a negative pressure between30 kPa and 6 kPa, preferably a negative pressure between 20 kPa and 8kPa, and more preferably a negative pressure between 15 kPa and 8 kPa ,and with an orifice 40 an airflow of more than 50 l/s, preferably morethan 60 l/s, and more preferably more than 70 l/s. This specialcharacteristic of the motor-fan unit differs from the characteristic ofmotor-fan units used in conventional vacuum-cleaning apparatus in thatthe latter generate an essentially higher negative pressure and anessentially lower maximum airflow. Surprisingly, it has shown that suchmotor-fan units are particularly energy-saving in use, yet fulfill therequirements on a constant airflow of sufficient power.

According to a particularly preferred further development of allinventions described above the vacuum cleaner may have, with an orifice8 (40 mm), a rate of airflow of more than 250 W, preferably of more than300 W, more preferably of more than 350 W. If the invention isconstructed in this way a fully satisfying vacuuming operation isensured during the complete filling of the filter bag.

Preferably, the motor-fan unit may have, with an orifice 8 (40mm), anefficiency according to EN 60335 of at least 20%, preferably of at least25%, and more preferably of at least 30%. This further development ofthe invention results in a particularly energy-saving vacuum-cleaningapparatus.

According to another further development of all inventions describedabove the vacuum cleaner may comprise a filter bag change indicatorindicating it during the vacuum-cleaning, the airflow drops under thesubstantially constant value for a predetermined period, To this end, inparticular the sensors can be applied that are provided for measuringthe controlled variables.

According to another preferred further development of theabove-described inventions the filter bag has a volume in a range of 1.5l to 8 l measured according to EN 60312. Filter bags of this type areprimarily used in vacuum cleaners that are constructed as canistervacuum cleaners, hand-held vacuum cleaners, wetidry vacuum cleaners oruprights for domestic use.

BRIEF DESCRIPTION OF THE FIGURES

The figures serve to explain the prior art and the invention, in which

FIG. 1 and

FIG. 2 show filter bags according to the prior art with surface folds;

FIG. 3 shows the reduction of the airflow for vacuum-cleaning apparatuscomprising vacuum cleaners and filter bags according to the prior art aswell as for a vacuum-cleaning apparatus without filter bag according tothe prior art;

FIG. 4 shows the air characteristics for a motor-fan unit used invacuum-cleaning apparatus according to the prior art;

FIG. 5 shows the air characteristics for a motor-fan unit not used invacuum-cleaning apparatus according to the prior art, which isparticularly suited for implementation in the present invention; and

FIG. 6 shows the airflow and electric input power of a first and asecond embodiment of the present invention.

EMBODIMENTS OF THE INVENTION

FIG. 5 shows the characteristic curve of the motor-fan unit according toan embodiment of the invention. Same is characterized by a comparativelylow maximum negative pressure with an orifice 0, and a high volume flowwith orifice 9 (50 mm). Especially with orifice 0 a negative pressure of14.3 kPa is obtained. Orifice 9 (50 mm) results in an airflow of 86.5dm3/s. Hence, the characteristic curve is very flat. With the maximumairflow the motor consumes a power of 1240 W. The airflow power (productof negative pressure and airflow) amounts to a maximum of 498 W withorifice 7 (30 mm).

FIG. 4, however, shows the characteristic data for a motor-fan unit asused according to the prior art in vacuum-cleaning apparatus. Withorifice 0 the motor-fan unit generates a negative pressure of 35.8 kPa,orifice 9 (50 mm) results in an airflow of 53.5 dm³/s. Hence, thecharacteristic curve of the fan is very steep. With the maximum airflowthe motor consumes a power of 1900 W. The airflow power is 614 W. In thecase of greatly dogged paper filter bags such a design had beennecessary and sensible.

In the particularly preferred embodiment of the present invention filterbags with surface folds are used as are described in the above chapterDEFINITIONS.

The motor-fan unit shown in FIG. 5, in combination with a filter baghaving surface folds and an installation space adapted to the filterbag, allows with a corresponding automatic controlling of the airflowthe realization of a vacuum cleaner that achieves a high, constantairflow with an input power of below 1000 W. FIG. 6 shows the resultsfor two embodiments according to the present invention, both having incommon that a very high, constant airflow is achieved with a lowelectric input power.

1. Vacuum-cleaning apparatus comprising a vacuum cleaner and a filterbag made of non-woven fabric, wherein the vacuum cleaner has a nominalelectric input power of less than 1200 W the vacuum cleaner comprises amotor-fan unit and a controlling device controlling the vacuum cleanersuch that the airflow is kept substantially constant at a value of atleast 34 l/s, when the filter bag is loaded with DMT8 test dustanalogous to EN 60312, and the filter bag is a disposable filter bagmade of non-woven fabric which has an airflow drop of less than 15 intests demonstrating a reduction of a maximum airflow with a partiallyfilled dust container analogous to EN
 60312. 2. The apparatus accordingto claim 1, wherein the controlling device is an electronic controllingdevice adapted to control an electric input power of the motor-fan unit,3. The apparatus according to claim 2, wherein an increase of the inputpower of the motor-fan unit required to maintain the substantiallyconstant airflow when the filter bag is loaded with DMT8 dust analogousto EN 60312 is not more than 35% in relation to the input power of themotor-fan unit when the filter bag is empty.
 4. The apparatus accordingto claim 1, wherein the motor-fan unit comprises a reluctance motor. 5.The apparatus according to claim 1, wherein the controlling devicecomprises a throttle valve provided to control the airflow to besubstantially constant.
 6. The apparatus according to claim 1, whereinthe controlling device is adapted such that a negative pressuredownstream of the filter bag is used as a controlled variable.
 7. Theapparatus according to claim 1, wherein the controlling device isadapted such that a negative pressure upstream of the filter bag is usedas a controlled variable,
 8. The apparatus according to claim 1, whereinthe controlling device is provided such that the flow rate measured atan optional position in the flow path is used as a controlled variable.9. The apparatus according to claim 1, wherein the filter bag is a flatbag.
 10. The apparatus according to claim 1, wherein the filter bagcomprises at least one surface fold.
 11. The apparatus according toclaim 1, wherein the motor-fan unit is adapted such that the vacuumcleaner generates, with a filter bag being inserted, with an orifice 0 anegative pressure between 30 kPa and 6 kPa, and with an orifice 8 (40mm) an airflow of more than 50 l/s.
 12. The apparatus according to claim1, wherein the vacuum cleaner has, with an orifice 8 (40 mm), a rate ofairflow of more than 250 W.
 13. The apparatus according to claim 1,wherein the motor-fan unit has, with an orifice 8 (40 mm), an efficiencyaccording to EN 60312 of at least 20%.
 14. The apparatus according toclaim 1, wherein the vacuum cleaner comprises a filter bag changeindicator indicating if, during the vacuum-cleaning, the airflow dropsunder a substantially constant value for a predetermined period.
 15. Theapparatus according to claim 1, wherein the filter bag has a volume in arange of 1.5 l to 8 l measured according to EN
 60312. 16. The apparatusaccording to claim 1, wherein the vacuum cleaner has a nominal electricinput power of less than 900 W.
 17. The apparatus according to claim 1,wherein the airflow is kept substantially constant at a value of atleast 40 l/s.
 18. The apparatus according to claim 1, wherein thedisposable filter bag made of non-woven fabric which has an airflow dropof less than 5% in tests demonstrating the a reduction of the a maximumairflow with a partially filled dust container analogous to EN 60312.19. The apparatus according to claim 3, wherein the increase of theinput power of the motor-fan unit required to maintain the substantiallyconstant airflow when the filter bag is loaded with DIMT8 dust analogousto EN 60312 is not more than 15% in relation to the input power of themotor-fan unit when the filter bag is empty.
 20. The apparatus accordingto claim 4, wherein the motor-fan unit comprises a switched reluctancemotor.